Calamitic metallomesogens derived from unsymmetric pyrazoles

Three series of copper(II) complexes 1a–1c derived from unsymmetric pyrazoles 2a–2c were prepared and their mesomorphic properties investigated. The mesomorphic behavior of compounds was studied by differential scanning calorimetry, polarizing optical microscopy, and powder X-ray diffractometry. The crystal and molecular structures of mesogenic copper complex (2a; n=10) of 3-[4-decyloxyphenyl]-1H-pyrazole were determined by means of X-ray structural analysis. It crystallizes in the triclinic space group P-1, with a=4.0890(1) Å, b=18.0167(2) Å, c=25.5015(5) Å, and Z=2. The geometry at copper center was not perfectly square planar. A weak intermolecular H-bond (d=2.36 Å) between Cl1 and H2 atoms and π–π interaction (ca. 3.45–3.55 Å) was also observed. All their precursors 2a–2c were not mesogenic. In contrast, copper complexes 1a formed nematic or smectic C phases and complexes 1b–1c formed crystalline phases. Powder X-ray diffraction experiments confirmed the presence of SmC phase.